DRI Spring Newsletter 2007

	http://www.dri.edu
	Spring 2007

Solving Problems—DRI Studies Agricultural Water-Conservation Technique
(continued from homepage...)

DRI faculty member Dr. Rick
Susfalk drills a hole in Kannah Creek Ditch #2 for installation of water monitoring equipment.

Many farmers and municipalities in the western U.S. depend on water-delivery systems such as canals and ditches to transport water for use on crops and in other agricultural-related activities. Many of these waterways are not lined, so water is often lost because of seepage through the bottoms and sides. Since early 2005, a multi-disciplinary team of scientists from DRI and other institutions has been studying the use of a chemical substance, polyacrylamide (PAM), to reduce seepage from water-delivery canals and ditches. Drs. Rick Susfalk and Michael Young, co-principal investigators on the project, are leading a team of faculty, staff and students from DRI’s Divisions of Hydrologic Sciences and Earth and Ecosystem Sciences, to better understand the water conservation benefits and potential environmental risks associated with using PAM to reduce water loss in unlined canals. Their work is a collaborative effort, also involving the University of Nevada, Reno, the University of Nevada, Las Vegas, Colorado State University, Water Solutions of Colorado, Hydrologic Solutions, LLC, and the U.S. Bureau of Reclamation (Reclamation).

Max Schmidt applies PAM to Smith Ditch, near Grand Junction, Colo.
photo by Dr. Duane Moser

Polyacrylamide is a synthetic chemical that belongs to a class of long-chain polymers. These polymers are used in applications as diverse as food packaging, paper manufacturing, wastewater treatment, drilling fluids for oil wells, and as a soil amendment to reduce erosion. One form of PAM sometimes found in homes is used to improve the water-retention properties of soil. Though this form of PAM is not used in water-delivery canals, it illustrates the diversity of this molecule. The molecular structure of PAM used in canal systems is slightly different, and it has properties that allow it to react with silt- and clay-sized sediment suspended in the canal water. After sufficient reaction time, the sediment-laden PAM molecule settles to the bottom of the canal and partially seals it.

DRI faculty were asked by Reclamation, through the Water 2025 program, to examine under what conditions does PAM reduce seepage. Tests were conducted on several scales, from lab-scale experiments completed at DRI, to full-scale experiments conducted in irrigation canals in Colorado and Montana. During 2006 alone, DRI faculty and their collaborators conducted almost a dozen full-scale canal experiments. The experimental design included a significant collection of data to measure reduction in canal seepage and water samples to detect the possible presence of PAM and other residual compounds in the canal water. Preliminary results showed that PAM does seal canals and ditches when the canal conditions are favorable, reducing seepage in some cases by over 90 percent. Depending on field conditions, PAM could be a good choice for canal operators for treating their ditches, but there are other aspects of PAM use that need to be investigated if Reclamation recommends it for widespread use.

DRI technician Brian Fitzgerald collects a macroinvertebrate sample from Smith Ditch, near Grand Junction, Colo.
photo by Brian Epstein

DRI technician Brian Fitzgerald collects a macroinvertebrate sample from Smith Ditch, near Grand Junction, Colo.
photo by Delbert Smith

DRI was also asked by Reclamation to examine possible human health and environmental impacts in the use of PAM. The primary human health concern is that acrylamide, a suspected human carcinogen, is present in low concentrations in PAM and released into the canal water when PAM is used. Through the use of laboratory analyses of acrylamide from samples collected during canal treatment, to the recent completion of a Risk Characterization report on PAM use, DRI faculy showed that potential health risks from PAM use were extremely low. Another factor being considered is whether PAM use could have negative impacts to established aquatic life that might be living in the canal, or in streams that might receive water from the canal. These experiments are ongoing.

In some cases, PAM might not be a good choice to reduce seepage. For example, seepage-dependent wetlands that have been established through years of slow leakage through the canals and ditches might lose their source of water if the canals are sealed. So, there are many factors to consider, not just how well PAM might or might not work to stop water loss.

With the extensive field experiments already conducted in 2006, and additional experiments being conducted in 2007, DRI faculty are using these data to simulate the transport of PAM in canal systems to better predict the distance this chemical might travel from where it is applied. In addition, possible environmental impacts are being evaluated to see what effects, if any, applications of PAM would have on aquatic life. In trying to make more efficient use of the water delivered for agriculture in the West, DRI faculty are exploring all aspects of use of the PAM polymer in irrigation waterways.